Vacuum Insulated Structure With End Fitting And Method Of Making Same

ABSTRACT

A vacuum insulated structure including a tube having an outer wall, a jacket surrounding the tube to enclose an annular insulating space, the jacket having an end that terminates at the outer wall of the tube, a seal formed between the end of the jacket and the tube to preserve a vacuum within the insulating space, and a fitting affixed to one of the tube and the jacket for coupling the vacuum insulated structure to an external device. A method of making a vacuum insulated structure including forming a tube and a jacket, positioning the jacket over the tube to form an annular insulating space, with an end of the jacket being positioned adjacent to an outer wall of the tube to form a vent, causing air to escape through the vent, sealing the vent, and affixing a fitting to one of the tube and the jacket.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/547,749, “Vacuum Insulated Structure With End Fitting And Method OfMaking Same” (filed Aug. 22, 2019, and now allowed), which is acontinuation of U.S. patent application Ser. No. 15/841,427, “VacuumInsulated Structure With End Fitting And Method Of Making Same” (filedDec. 14, 2017, and now issued as U.S. Pat. No. 10,495,250), which is acontinuation of U.S. patent application Ser. No. 14/953,756, “VacuumInsulated Structure With End Fitting And Method Of Making Same” (filedNov. 30, 2015, and now issued as U.S. Pat. No. 9,874,303) which is adivisional of U.S. patent application Ser. No. 13/644,199, “VacuumInsulated Structure With End Fitting And Method Of Making Same” (filedOct. 3, 2012, and now issued as U.S. Pat. No. 9,243,726). The entiretiesof the foregoing applications and patents are incorporated by referenceherein for any and all purposes.

TECHNICAL FIELD

The present disclosure relates to the field of vacuum-insulatedstructures and methods of fabricating such structures.

BACKGROUND

Vacuum insulated structures have many practical uses and can beconstructed as described, for example, in U.S. Pat. Nos. 7,681,299 and7,374,063, in which tube walls and jacket walls are vacuum brazedtogether to create a strong metallurgical joint that has a highermelting temperature than the braze material itself. Typically, the tubewalls and the outer jacket walls of such vacuum insulated structures arequite thin, often less than about 0.010″ inches. Consequently, it can bedifficult to affix a fitting onto a vacuum insulated structure to enablethe structure to be mounted or supported by an external device. Inparticular, an attempt to weld or solder a fitting to a tube wall or theouter jacket wall of the structure risks perforating the thin wall anddestroying the vacuum seal. Additionally, acid that is commonlycontained in solder materials can erode into and eventually perforatethe thin outer jacket wall. Further, the thin walls of the vacuuminsulated structure may not be capable of supporting a threaded orcompression-type fitting without sustaining damage.

SUMMARY

An embodiment of a vacuum insulated structure is described, thestructure including a tube having an outer wall and a jacket surroundingthe tube to enclose an annular insulating space between the tube and thejacket. The jacket has an end that terminates adjacent to the outer wallof the tube. A seal is formed between the end of the jacket and theouter wall of the tube to preserve a vacuum within the insulating space.A fitting is affixed to one of the tube and the jacket for coupling thevacuum insulated structure to an external device. The fitting may beaffixed at any point along the length of the jacket, including near oneof the ends of the jacket or at an intermediate portion along thejacket. Alternatively, the fitting may be affixed on the outer wall ofthe tube beyond the jacket.

In one variation, the seal is formed by a first brazing process and thefitting is affixed by a second brazing process. The two brazing processmay be performed concurrently. Alternatively, the two brazing processesmay be performed sequentially, first sealing the vent and then affixingthe fitting.

The fitting may be any type of fitting, including but not limited to awelding socket, a female threaded fitting, a male threaded fitting, acompression fitting, a flange fitting, a custom fitting, andcombinations thereof.

An embodiment of a method of making a vacuum insulated structure with afitting is described. The method includes forming a tube having an outerdiameter defined by an outer wall and forming a jacket having an end andan inner diameter at least slightly larger than the outer diameter ofthe tube. The jacket is positioned over the tube to form an annularinsulating space between the jacket and the tube, with the end of thejacket being positioned adjacent to the outer wall of the tube to form avent between the end of the jacket and the outer wall of the tube. Avacuum is drawn on the annular insulating space by causing air toevacuate the space through the vent, and the vent is then sealed topreserve the vacuum within the insulating space. Finally, a fitting isaffixed to one of the tube and the jacket.

In one variation, sealing the vent includes positioning a bead of firstbraze material within the insulating space adjacent to the vent, heatingthe tube to cause the bead of first braze material to flow into the ventand form a joint between the tube and the jacket, and allowing the jointto cool, thereby sealing the vent.

In a further variation, affixing the fitting includes positioning a beadof second braze material between an inner surface of the fitting and anouter wall of the jacket, heating the jacket to cause the bead of secondbraze material to melt and form a joint between the jacket and thefitting, and allowing the joint to cool, thereby fusing the fitting tothe jacket.

The steps of heating the tube and heating the jacket may be performedconcurrently or sequentially; if sequentially, heating the tube andsealing the vents is preferable performed before heating the jacket andaffixing the fitting. In one embodiment, evacuation of the insulatingspace and brazing is conducted in a vacuum oven.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of the disclosedembodiments will be more apparent from the following more particulardescription thereof, presented in conjunction with the followingdrawings wherein:

FIGS. 1A and 1B are a side view and a side cross-sectional view,respectively, showing an embodiment of a vacuum insulated structure witha fitting;

FIGS. 2A and 2B are a side view and a side cross-sectional view,respectively, of another embodiment of a vacuum insulated structure witha fitting;

FIGS. 3A-3D are side cross-sectional views illustrating a method ofassembling a vacuum insulated structure with a fitting; and

FIGS. 4A-4C are side or axial cross-sectional views illustrating anotherembodiment of a vacuum insulated structure with different types offittings; and

FIGS. 5A and 5B are side views of another embodiment of a vacuuminsulated structure with a fitting.

DETAILED DESCRIPTION OF THE DRAWINGS

Two embodiments of a vacuum insulated structure 10 are shown in FIGS.1A-1B and 2A-2B. Those embodiments are merely illustrative, it beingunderstood that infinite other embodiments may be constructed having thesame features as described herein.

The structure 10 includes a tube 20 having an inner wall 23, a jacket 30surrounding at least a portion of the tube 20 and having at least oneend 32, and a fitting 40 affixed to the jacket 30. In the depictedembodiments, the tube 20 is an elongate tube with a length many timesits diameter. The jacket 30 has a geometry similar to that of the tube20, to form a narrow annular space between the tube 20 and the jacket30. However, the same principles of construction as described herein maybe applied to a tube 20 of any shape with a correspondingly shapedjacket 20 and annular space. For example, the tube 20 and the jacket 30may be generally spherical in shape.

In the embodiments as shown, the tube 20 has an outer diameter definedby an outer wall 22 of the tube 20. The jacket 30 has an inner diameterthat is at least slightly larger than the outer diameter of the tube 20,so that an annular insulating space 36 is formed between the tube 20 andthe jacket 30. The annular insulating space 36 is formed as a volumethat will be put under vacuum, whereas the tube interior 26 can formedfor accommodating devices, materials, or components that are desired tobe insulated by annular insulating space 36, for example a surgicalprobe, or a cooling device for infrared imaging electronics. Structure10 can also be used for, but is not limited to, insulating andinstalling aviation electronics and instruments for transporting tubesfor oil, for transporting and storing fuel for hydrogen fuel cells, asthermal insulation for spacecraft components such as electronics, forthermal control of components of weapon systems. In particular,structure 10 is particularly suitable when devices or materials have tobe insulated from effects of very large changes in temperature. Forexample, when insulating space craft electronics, the temperaturedifference may be in a range between −200.degree. C. and +150.degree.C., and structure 10 can be exposed to temperature difference of about.DELTA.600.degree. C.

With FIGS. 3A-3B an exemplary method of making the vacuum inside tubeinterior 26 is shown. The annular insulating space 36 may be evacuatedthrough a vent 34 located adjacent to the end 32 of the jacket 30. Asshown, the vent 34 is a small gap between the end 32 of the jacket 30and the outer wall 22 of the tube 20. The insulating space 30 may beevacuated by placing the entire structure 10 into a vacuum chamber andthen drawing a vacuum in the chamber. As the pressure in the vacuumchamber decreases, gas (usually air) escapes from the insulating space36 via the vent 34. Other methods for applying suction to the vent 34may alternatively be used.

In one embodiment, the evacuation of the insulating space 36 achieves apressure lower than the pressure applied to the vent 34 (i.e., the levelof vacuum achieved in the vacuum insulating space 36 is deeper than thelevel of vacuum applied to the vent 34) as a result of the geometry ofthe walls bounding the vacuum insulating space 36 in the vicinity of thevent 34. In particular, the ends 32 of the jacket 30 are configured inthe vicinity of the vents 34 to preferentially direct gas moleculestoward the vent 34 in an ultra-low pressure free molecular flow regimein which the frequency of gas molecule collisions with the walls exceedsthe frequency of gas molecule collisions with each other. The relativegeometry of the jacket 30 and the tube 20 at the jacket ends 32 adjacentto the vent 34 has a guiding effect on gas molecules in a free molecularflow regime so that the flux of gas molecules out the vent 34 is greaterthan the flux of gas molecules into the vent 34. A highly insulatingspace having a low vacuum created by such geometry can be used indevices of miniature scale or in devices having insulating spaces ofextremely narrow width. For example, insulating spaces 30 have beencreated incorporating this geometry with gaps on the order of 0.004″ orsmaller.

In gases under relatively modest vacuums, for example at pressures equalto or greater than about 10.sup.-2 torr at about 70.degree. F.,molecule-to-molecule collisions dominate such that the number ofinteractions between the gas molecules themselves is large in comparisonto the number of interactions between the gas molecules and the walls ofa container for the gas molecules. In this circumstance, Maxwell's gaslaw accurately describes the molecular kinetic behavior of gasmolecules. However, at greater (deeper) levels of vacuum, for example aspressures less than about 10.sup.-2 torr, and particularly at pressuresless than about 10.sup.-4 torr at about 70.degree. F., a free molecularflow regime takes over because the scarcity of gas molecules causes thenumber of interactions between the gas molecules and the walls of thecontainer to be large in comparison with the interactions between thegas molecules themselves. At such low pressures, the geometry of a spaceto which vacuum is applied becomes a controlling factor in the rate atwhich gas molecules exit the space via a vent as compared with the rateat which gas molecules enter the space via the vent.

While vacuum is being applied to the vent 34, the structure 10 may beheated to accelerate the motion of the gas molecules within theinsulating space 36, so as to further bias the flux of gas moleculesoutward from the vent 34 as compared with inward into the vent 34. Forexample, tube 20 or the structure 10 may be heated to an elevatedtemperature and held at that temperature for a period of time during theevacuation process. Longer hold times may be used to further increasethe vacuum achievable in the insulating space 36.

Once a desired level of vacuum has been achieved in the insulating space36, the vent 34 is sealed to maintain the vacuum. In one embodiment, thevent 34 is sealable by a first braze material 24 that melts and flowsinto the vent 34 when heated to a brazing temperature, so that the end32 of the jacket 30 is brazed to the outer wall 22 of the tube and theinsulating space 36 is sealed off. The use of brazing to seal theevacuation vent of a vacuum-sealed structure is generally known in theart. To seal the vent 36, a bead of first braze material 24 ispositioned on the outer wall 22 of the tube 20, slightly within theinsulating space 36, near the vent 34 and the end 32 of the jacket, asshown in FIG. 3A. Prior to heating, the bead of first braze material 24is solid and is preferably adhered to the outer wall 22 of the tube 20.For high vacuum applications, the first braze material is preferablyfree from flux, since flux can off-gas after brazing, thereby reducingthe vacuum within the insulating jacket 36.

The first braze material 24 is positioned between the tube 20 and thejacket 30 near the vent 34 in such a manner that during the evacuationprocess (i.e., prior to the brazing process) the vent 34 is not blockedby the braze material 24. Toward the end of the evacuation process, asthe desired level of vacuum is being achieved in the insulating space36, sufficient heat is applied to the tube 20 or to the entire structure10 to melt the first braze material 24 such that it flows by capillaryaction into the vent 34. The flowing braze material 24 seals the vent 34and blocks the evacuation path from the insulating space 36, as shown inFIG. 3B. Flowing of the first braze material 24 is facilitated by anypreheating that occurs by heating of the tube 20 or the structure 10during the evacuation phase in order to enhance the ultimate level ofvacuum achieved in the insulating space 36. After maintaining asufficient temperature for a sufficient amount of time, the first brazematerial forms an alloyed joint between the tube 20 and the jacket 30.The joint formed by the first braze material 24 is then allowed to cool,so as to solidify and seal the vent 34 closed. Alternatively, otherprocesses can be used for sealing the vent 34, including but not limitedto a metal surgical process or a chemical process.

Fitting 40 may be attached to the structure 10, either to the tube 20 orto the jacket 30. FIGS. 3C and 3D depict a method of attaching a fitting40 to jacket 30. In the depicted embodiments, the fitting 40 is attachedto the jacket 30, noting that essentially the same process can be usedfor attachment to the tube 20 or the jacket 30. First, as shown in FIG.3C, the fitting 40 is slipped over the end 32 of the jacket 30 and abead of second braze material 44 is positioned between an outer wall 38of the jacket 38 and an inner surface 42 of the fitting 40. Although thedepicted fitting 40 is a weld or braze socket, it is understood that thefitting 40 may be any fitting that enables attachment of the structure10 to another device, and may include but is not limited to a weldsocket, a braze socket, a threaded fitting, a compression-type fitting,a flange fitting, a custom fitting, and the like.

Once the fitting 40 and the bead of second braze material 44 arepositioned as desired with respect to the jacket 30, sufficient heat isapplied to the jacket 30 or to the entire structure 10 to melt thesecond braze material 44. After maintaining a sufficient temperature fora sufficient amount of time, the second braze material forms an allowedjoint between the jacket 30 and the fitting 40. The second brazematerial may be the same as or different from the first braze material.The joint formed by the second braze material 44 is then allowed tocool, so as to solidify and secure the fitting 40 to the jacket 30.Although when affixing the fitting it is not necessary to use a secondbraze material 44 that does not off-gas, it is still preferable to use aflux-free second braze material to avoid any acid corrosion or pittingthat can eventually penetrate the thin jacket wall 30. Fitting 40 shownhas an L-shape from a cross-sectional view, and can be used to attachstructure 10 to a bracket (not shown).

Alternatively, fittings 50, 60, 70, and 80 can be arranged at the tubeinterior 26 on the inner wall 23, and a similar attachment process canbe used as described for fitting 40. For example, FIG. 4A shows afitting 50 on the left side of tube 20, having a hollow structure andbeing threaded for engaging with a treaded rod or screw. On the rightside of FIG. 4A, another fitting 60 is illustrated, comprised of webs 62that hold a nut 64 substantially in the center of tube 20, as shown inthe cross-sectional view of FIG. 4B. Nut 64 may have a thread in theinner bore with or without a thread. Nut 64 could also just be a threadbore, as in fitting 50.

FIG. 4C shows a fitting 70 arranged on the left side of the tube 20,having a blocking body 72 and a threaded rod 74 protruding in an axialdirection away from tube 20. In addition, a fitting 80, illustrated onthe left side of the figure can be formed as a nut or another structurewith a bore. Fittings 50, 60, 70, and 80 can be used for variousattachment purposes. For example, fittings 50, 60, 70, and 80 can beused to attach structure 10 to another tube, to an additional casing orinsulating structure, or for connection with dewars.

FIG. 5A shows an alternative embodiment in which the fitting 90 isarranged directly onto the tube 20 by use of braze material 94, and islocated between tube 20 and jacket 30 as a spacer. In the variant shown,fitting 90 is made of a hollow concentric structure having an innerdiameter that is slightly bigger than the outer diameter of tube 20, sothat fitting 90 can be placed over tube 20 for brazing, or by anothersealed attachment procedure. Fitting has a narrowed protrusion that isthreaded, allowing to secure the structure 10 to a corresponding thread.Also, in the variant shown, jacket 30 is affixed to tube 29 on one side,and on the other side is affixed to the fitting 90. It is also possiblethat two fittings 90 are concentrically arranged at two differentlocations of tube 20, and that the jacket 30 is not directly attached tothe tube 20, but to fittings 90.

FIG. 5B is an exemplary method of making the vacuum inside the annularinsulating space 36, similar to the method shown with respect to FIG.3A. Space 36 can be evacuated through a vent 34 located adjacent to theend 32 of the jacket 30 and the outer peripheral wall of fitting 90.Before the evacuation, the front end of jacket is brazed to tube 20 withmaterial 24. The insulating space 30 may be evacuated by placing theentire structure 10 into a vacuum chamber and then drawing a vacuum inthe chamber. As the pressure in the vacuum chamber decreases, gasescapes from the insulating space 36 via the vent 34. Other methods forapplying suction to the vent 34 may alternatively be used.

The foregoing describes the invention in terms of embodiments foreseenby the inventors for which an enabling description was available,notwithstanding that insubstantial modifications of the invention, notpresently foreseen, may nonetheless represent equivalents thereto.

What is claimed:
 1. A vacuum insulated structure, comprising: a vessel,the vessel having an outer surface and an inner surface, and the innersurface defining a lumen; a jacket, the jacket being arranged about thevessel and the jacket having an outer surface and an inner surface; anda first fitting, the first fitting being sealed to the vessel and thefirst fitting being sealed to the jacket, the structure defining asealed insulating space between the vessel and the jacket, a portion ofthe first fitting extending into the sealed insulating space, and thesealed insulating space being at less than atmospheric pressure.
 2. Thevacuum insulated structure of claim 1, wherein the jacket comprises aregion that converges toward the vessel.
 3. The vacuum insulatedstructure of claim 1, wherein the jacket comprises a region thatconverges toward the first fitting.
 4. The vacuum insulated structure ofclaim 1, wherein the first fitting comprises a threaded region.
 5. Thevacuum insulated structure of claim 1, wherein an edge of the jacket issealed to the vessel.
 6. The vacuum insulated structure of claim 1,wherein an edge of the jacket is sealed to the first fitting.
 7. Thevacuum insulated structure of claim 1, wherein the vessel comprises aclosed end.
 8. The vacuum insulated structure of claim 1, wherein thevessel extends in an axial direction, and wherein the first fitting hasa cross-sectional dimension that varies along the axial direction. 9.The vacuum insulated structure of claim 1, wherein the first fitting ischaracterized as having a L-shaped cross-section.
 10. The vacuuminsulated structure of claim 1, wherein the first fitting comprises abore therethrough.
 11. The vacuum insulated structure of claim 1,wherein the first fitting is characterized as a welding socket, a femalethreaded fitting, a male threaded fitting, a compression fitting, aflange fitting, a custom fitting, or any combination thereof.
 12. Thevacuum insulated structure of claim 1, further comprising a secondfitting.
 13. A workpiece, comprising: a vessel, the vessel having anouter surface and an inner surface, and the vessel having a lumendefined by the inner surface; a jacket, the jacket being arranged aboutthe vessel and the jacket having an outer surface and an inner surface;a fitting; a first amount of sealing material disposed between thefitting and the jacket, the vessel extending in an axial direction, thefitting extending in the axial direction, and the first amount ofsealing material being disposed at an intermediate location on thefitting in the axial direction; and a second amount of sealing materialdisposed between the fitting and the vessel;
 13. The workpiece of claim12, wherein the vessel is characterized as a tube.
 14. The workpiece ofclaim 12, wherein the fitting is positioned at an end of the jacket. 15.The workpiece of claim 12, wherein the fitting is affixed at anintermediate position along the jacket.
 16. The workpiece of claim 12,wherein the first amount of sealing material or the second amount ofsealing material comprises a braze material.
 17. The workpiece of claim16, wherein the first amount of sealing material and the second amountof sealing material comprise different braze materials.
 18. Theworkpiece of claim 12, wherein the jacket comprises a region thatconverges towards the vessel.
 19. The workpiece of claim 12, wherein thejacket comprises a region that converges towards the fitting.
 20. Amethod, comprising: arranging a jacket and a vessel such that the jacketis arranged about the vessel; arranging a fitting such that at least aportion of the fitting is disposed between the jacket and the vessel;and sealing the jacket to the fitting and sealing the fitting to thevessel so as to define a sealed insulating space between the jacket andthe vessel, the fitting being arranged such that at least a portion ofthe fitting extends into the sealed insulating space, and the sealedinsulating space being at less than atmospheric pressure.